Electromechanical actuators

ABSTRACT

The invention concerns an electromechanical actuator comprising at least an electric motor ( 1 ), as well as coupling ( 4 ) and gear reduction ( 4 ) means, which drive an output shaft ( 11 ). The invention is characterized in that the coupling and gear reduction means mesh with a crank plate ( 7 ) designed to be driven in rotation with an angular travel limited by two stops, a small connecting rod ( 9 ) being articulated to one end on a crank pin ( 8 ) of said crank plate and being articulated at its other end on a long connecting rod ( 10 ) which is itself integral with the output shaft, the two ends of said long connecting rod being respectively guided in displacement each along a guide, and the displacement angle between said two stops is more than 180°, the movements of the rod being structurally locked in case of overriding, the crank plate being immediately proximate to one of its travel limit stops.

GENERAL FIELD AND PRIOR ART

This invention relates to electromechanical actuators.

It is advantageously used for the actuators equipping aircraft landinggear uplock boxes and their doors.

The overall purpose of the proposed device, in particular, is to ensurethe mechanical unlocking operation in back-up mode, enabling extensionof the landing gear by gravity.

DISCLOSURE OF THE INVENTION

The proposed solution is based, in particular, on the use of proventechnologies but, in comparison with traditional solutions, theimplementation of said solution enables a weight advantage, a simpledesign, and a reduced current consumption. Besides its direct impact,the reduced weight makes it possible to reduce the mechanical stressesrelated to the high accelerations during use. The simple design and thereduced number of parts make it possible to guarantee a high level ofreliability. Finally, the reduced consumption due to the actuator's highefficiency, not only has an advantage with respect to the generator, butalso prevents overheating and stresses detrimental to a good level ofreliability.

More precisely, the invention proposes an electromechanical actuatorcomprising at least one electric motor, as well as coupling and gearreduction means, which drive an output shaft,

-   -   characterized in that said coupling and gear reduction means        mesh with a crank plate designed to be driven in rotation with        an angular travel limited by two stops, a small connecting rod        being articulated at one end to a crank pin of said crank plate        and being articulated at its other end to a long connecting rod        which is itself integral with the output shaft, the two ends of        said long connecting rod each being guided respectively in their        travel along a guide, and in that the displacement angle between        said two stops is greater than 180°, the movements of the        connecting rod being structurally locked when, following an        override, the crank plate is situated directly adjacent to one        of its travel limit stops.

DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomefurther apparent from the following description, which is purelyillustrative and non-limiting and which must be read with reference tothe appended drawings in which:

FIGS. 1 and 2 are kinematic chains showing a first possible embodimentof the invention;

FIGS. 3 and 4 are kinematic chains showing another possible embodimentof the invention;

FIGS. 5 and 6 are perspective schematic representations of the travel ofthe connecting rod in the embodiment of FIGS. 3 and 4;

FIG. 7 is the angular displacement curve of the connecting rod withrelation to the angular position of the crank plate.

DESCRIPTION OF ONE OR MORE EMBODIMENTS OF THE INVENTION

General Points

Two embodiments are described hereinbelow.

In both of these embodiments, notice is taken of the absence of adifferential and wheel/tangent screw. These choices enable:

-   -   Reliability (by the reduction in the number of parts and the        design),    -   Consumption (by a high motor/output efficiency),    -   Vibrating environment.

The actuator in accordance with the first embodiment has a particularlysimple design and a reduced number of parts.

It includes:

-   -   A three-phase asynchronous motor consisting of a squirrel-cage        rotor, an insulated double-winding stator, and stalling        protection. This motor is derived from “space” applications. The        moving parts are of normalized mass in order to tolerate        vibration and shocks.    -   A synchronous permanent magnet coupler making it possible to        disengage the motor when the actuator reaches the stop.    -   A high-efficiency reversible gear reducer.    -   An irreversible lever device, making it possible to ensure        irreversibility at the end-of-travel position. This device        eliminates the use of tangent screws detrimental to efficiency        and therefore the use of an “oversized” motor, and ensures a        positive irreversibility independent of the vibrations.

As for itself, the actuator in accordance with the second embodimentincludes the following elements:

-   -   Two conventional three-phase asynchronous motors.    -   Two couplers each consisting of a centrifugal coupler and a        synchronous coupler. These couplers make it possible to        disengage the motors when the actuator reaches the stop, and to        ensure operation in the event that the motor stalls. The use of        such devices makes it possible to provide:    -   A gear reducer and a lever device.

First Embodiment

The solution adopted makes it possible to use the same actuator for thevarious applications of uplock boxes known as “UPLOCKS”.

Of course, variants may be redesigned in relation to displacementtravel.

The diagram of the kinematic chain is shown in FIG. 1.

The three-phase asynchronous technology motor 1, powered with a 115-Voltalternating current having a variable frequency of between 360 and 800Hz, has a double stator winding and a single rotor. Each winding isseparate and electrically insulated.

This solution has the advantage of being much more reliable than anothermotor technology. In actuality, the number of parts and components isreduced in the assembly of the motor, in its control, and in its EMC/EMIfiltering. Moreover, the number of moving parts is limited to that whichis absolutely necessary, which is preferable to two motors coupled to adifferential gear train.

This device operates without any electronic circuit, which, inparticular, eliminates the disadvantages associated with the reliabilityand obsolescence of the active and passive components.

The single output shaft 3 is coupled directly to a torque limiter rep 4designed to absorb the shock of the abrupt stop of the kinematic chainelements when the output of the gear reducer or output shaft strikesagainst the mechanical stops in the end-of-travel position. This limiteralso enables the motor to continue to run when the gear reducer is idle,which safeguards the service life of the windings.

This magnetic technology torque limiter rep 4 has the advantage oftransmitting a weak torque and therefore that of having smalldimensions.

Furthermore, this technique has the advantage of considerably reducingthe dissipation of energy supplied by the motor when the output shafthas reached the stop position because the loss of synchronism bringsabout the magnetic breakdown and therefore the drop in transmissiontorque. The motor then runs almost in neutral.

The output of the torque limiter is equipped with a pinion rep 5 whichmeshes directly with the first stage of a straight-toothed gear reducerrep 6. In order to obtain a good level of efficiency for this gearreducer, the first stages are equipped with preloaded ball bearings. Theoutput stages have plain ring gauges.

The output pinion of the gear reducer meshes directly with a crank plate7 equipped with a toothed wheel and a crank pin 8. Said plate is drivenin a rotating movement the angular amplitude of which is limited toapproximately 200° by 2 stops integral with the body of the actuator.These mechanical stops enable a small connecting rod 9 of the plate 7 tobe locked in its end-of-travel position.

The head of this short small connecting rod 9 is articulated to thecrank pin of the crank plate 7. It imparts a rotating movement to theend of the long connecting rod 10 running between 2 guides. The otherend of this connecting rod is integral with the output shaft of theactuator in order to transmit a limited rotating movement (e.g., limitedto 12° to 13°).

This mechanical system forms a kinematic chain which is locked at theends of the angular travel.

In its counterclockwise rotation CCW, point B, symbolizing the crank pinof the plate, comes into contact with the mechanical stop CCW (this stopmaybe external to the actuator), after having bypassed point E (see theillustration in FIG. 2). Said point E is fixed in relation to theactuator housing and is the limit of travel physically representing thepossible non-return of the movement of the plate as a result of theaction of the small connecting rod, without encountering the stop CCW.

This system consisting of connecting rod+small connecting rod+plate+stopis thereby locked in the counterclockwise direction CCW by any movementcoming from the connecting rod, hence from the output shaft of theactuator, symbolized by point D (see the position in FIG. 2).

Only by reversing the direction of rotation of the plate 7, which iscapable of rotating clockwise, are the small connecting rod 9 and theconnecting rod 10 able to travel, and thereby unlock the kinematicchain.

Thus, said connecting rod travels first towards the stop external to theactuator by applying stress to the sub-assembly consisting of the smallconnecting rod+connecting rod; at that moment, the output shaft (pointD) is not rotating. This stress is absorbed by an elastic deformation ofone of the (appropriately shaped) parts making up the kinematic chain.Said deformation reaches its maximum when point B (crank pin) encounterspoint E, and decreases there beyond until it frees the output shaft torotate.

Thus, after having passed by point E (fixed in relation to the housing),the crank pin meets up again with the other stop CW by rotatingclockwise CW.

In its clockwise rotation CW, point B, symbolizing the crank pin of theplate, this time comes into contact with the mechanical stop CW (thisstop may be external to the actuator) after having bypassed point F (seeillustration in FIG. 3). Said point F is fixed in relation to theactuator housing and is the limit of travel physically representing thepossible non-return of the movement of the plate, as a result of theaction of the small connecting rod, without encountering the stop CW.

The system consisting of connecting rod+small connecting rod+plate+stopis thereby locked in its clockwise rotation CW by any movement comingfrom the connecting rod, hence from the output shaft of the actuator,symbolized by point D (see the position in FIG. 3).

Only by reversing the direction of rotation of the plate 7, which iscapable of rotating counterclockwise, are the small connecting rod 9 andthe connecting rod 10 able to travel, and thereby unlock the kinematicchain.

Thus, said connecting rod travels first towards the stop external to theactuator by applying stress to the sub-assembly consisting of the smallconnecting rod+connecting rod ; at that moment, the output shaft (pointD) is not rotating. This stress is absorbed by an elastic deformation ofone of the (appropriately shaped) parts making up the kinematic chain.Said deformation reaches its maximum when point B (crank pin) encounterspoint F, and decreases there beyond until it frees the output shaft torotate.

Thus, after having passed by point F (fixed in relation to the housing),the crank pin once again meets up with the other stop CCW by rotatingclockwise CCW.

Second Embodiment

As in the case of option 1, the principle adopted likewise consists inusing the same actuator for the 7 different applications of uplock boxesknown as “UPLOCKS”. If necessary, a variant may be redesigned todistinguish travel with an angular displacement of 13° in relation tothose of 14°.

The solutions implemented to ensure the actuator functions are presentedin the design described herein below:

The diagram of the kinematic chain is shown in FIG. 4 on the followingpage.

Two three-phased asynchronous technology motors rep 1 and 2, poweredwith a 115-Volt alternating current having a variable frequency ofbetween 360 and 800 Hz, has a single stator winding.

This solution has the advantage of being much more reliable than anothermotor technology. In actuality, the number of parts and components isreduced in the assembly of the motor, in its control and in its EMC/EMIfiltering. Moreover, the number of moving parts is limited to that whichis absolutely necessary, which is preferable to two motors coupled to adifferential gear train.

This device operates without any electronic circuit, which, inparticular, eliminates the disadvantages associated with the reliabilityand obsolescence of the active and passive components.

The output shaft of each of the motors is coupled directly to acentrifugal clutch 3, which makes it possible to disconnect the rotor ofa broken-down motor from the kinematic chain of the actuator. Thus, theworking motor is able to start without taking on the additional load ofthe defective motor.

The output of the centrifugal clutch is connected to a torque limiter 4designed to absorb the shock of the abrupt stop of the kinematic chainelements when the output of the gear reducer or output shaft strikesagainst the mechanical stops in the end-of-travel position. This limiteralso enables the motor to continue to run when the gear reducer is idle,which safeguards the service life of the windings.

This magnetic technology torque limiter rep 4 has the advantage oftransmitting a weak torque and therefore that of having smalldimensions.

Furthermore, this technique has the advantage of considerably reducingthe dissipation of energy supplied by the motor when the output shafthas reached the stop position because the loss of synchronism bringsabout the magnetic breakdown and therefore the drop in transmissiontorque. The motor then runs almost in neutral.

The output of each of the two torque limiters 4 is equipped with apinion rep S which meshes directly with the first stage of astraight-toothed gear reducer 6. In order to obtain a good level ofefficiency for this gear reducer, the first stages are equipped withpreloaded ball bearings. The output stages have plain ring gauges.

The output pinion of the gear reducer meshes directly with a crank plate7 equipped with a toothed wheel and a crank pin 8. Said plate isconnected to the clutch assembly enabling the irreversible locking ofthe output shaft rep 11 at the ends of its travel; this arrangement isidentical to that of the first embodiment.

The operation of the system of irreversibility is described above withrespect to the solution of the first embodiment.

Sample Dimensions

The speed reducing ratio is high and is calculated on the basis ofmotors having two pairs of poles:

N motor=10,500 rps for a slight slippage, i.e., 175 rps when thefrequency is at 360 Hz.

The output crank pin (rep 8 in FIG. 1) of the gear reducer must rotateat 0.24 rps.

Thus, the ratio is 175/0.24=729 for the gear reducer.

The gear reducer rep 6 consists of 4 stages:

-   -   R1 on the crank plate=5.8 (0.75-mm module);    -   R2=R3=R4=R5 (0.5-mm module) with identical staged wheels.

Thus, the speed reducing ratio is: 5.8×125=725.

The drive pinion (motor output) has 15 teeth.

The gear reducer efficiency is: 0.92×0.97×0.97×0.97=0.84

-   -   0.92 for R1    -   0.97 for R2, R3 and R4.

The efficiency of the connecting rod-crank system is:0.98×0.92×0.95=0.85

-   -   0.98 for the output shaft    -   0.92 for the connecting rod coupling (slider included)    -   0.95 for the crank    -   Hence, an overall mechanical efficiency of 0.89×0.88=0.71.

The input torque to be overcome is 60 NM (AT) in 2.5 seconds or else 120NM (2 AT) in much longer period of time.

The reduction of the connecting rod system is approximately 10.

In order to prevent the effects of unfeathering in the presence of themechanical environment (vibrations, shocks, jolts . . . ), a frictionaltorque for holding the crank in the stop position is provided on thefirst stage of the gear reducer, i.e., of approximately 0.001 NM. Thisfriction is produced by a magnetic device having permanent magnets.

The design basis of the motor for a single winding is as follows:

Torque to be produced under the worst conditions:(60/10/725/0.71)+0.001=0.013 NM.

1. Electromechanical actuator comprising at least one electric motor, aswell as coupling and gear reduction means, which drive an output shaft,characterized in that said coupling and gear reduction means mesh with acrank plate designed to be driven in rotation with an angular travellimited by two stops, a small connecting rod being articulated at oneend to a crank pin of said crank plate and being articulated at itsother end to a long connecting rod which is itself integral with theoutput shaft, the two ends of said long connecting rod each being guidedrespectively in their travel along a guide, and in that the displacementangle between said two stops is greater than 180°, the movements of theconnecting rod being structurally locked when, following an override,the crank plate is situated directly adjacent to one of its travel limitstops.
 2. Actuator as claimed in claim 1, characterized in that itincludes a double-stator asynchronous motor.
 3. Actuator as claimed inclaim 1, characterized in that it includes two asynchronous motors. 4.Actuator as claimed in claim 1, claim 2 or claim 3, characterized inthat the coupling means include a torque limiter.
 5. Actuator as claimedin claim 4, characterized in that said torque limiter is of the magnetictype.
 6. Actuator as claimed in claim 1, characterized in that thedisplacement angle of the crank plate between the two stops is of theorder of 200°.
 7. Actuator as claimed in claim 1, characterized in thatthe angular displacement possible for the connecting rod is of the orderof 12-13°.
 8. Actuator as claimed in claim 1, characterized in that thegear reduction means include first stages equipped with preloaded ballbearings.
 9. Actuator as claimed in claim 1, characterized in that thegear reduction means include output stages with plain ring gauges. 10.Actuator for a landing gear uplock box and/or for the doors of suchboxes, characterized in that it consists of an actuator as claimed inclaim 1.